According to the historical record dating back to 1895, 2012 was the hottest year this country has ever seen. But it's not just that the temperature has risen — from deadly tornadoes to the widespread coastal damage inflicted by Superstorm Sandy, we seem to be living through a period of intensified and heightened weather extremes.

Whether or not these harsh weather events are connected to global warming or are simply the random violence nature visits upon us is one of the central questions that environmental reporter Justin Gillis tackles in his "Temperature Rising" series for The New York Times. The series focuses on the arguments in the climate debate and examines the evidence for global warming and its consequences.

"It's an ongoing struggle for the scientists to puzzle out which of these things are linked and which ones aren't," Gillis tells Fresh Air's Dave Davies.

Gillis notes that there is "robust, healthy science" that provides evidence of climate change. Within the scientific mainstream, however, he says there is a considerable range of views about the risks we're running by causing what is essentially (on the geologic time scale) an instantaneous increase in carbon dioxide in the atmosphere. One such risk is rising sea levels. Gillis says experts believe sea levels will rise at least 3 feet in the next century, and that number could be as much as 6 feet.

"When I look at the scientific majority, the scientific mainstream," Gillis says, "I would say that as a group, they fear this is going to be pretty bad. They don't know exactly how bad it's going to get, and they don't know how fast it's going to get that [bad], which might be the ultimate question."

Interview Highlights

On how melting sea ice will affect land ice

"As we get less and less sea ice in the summer and more and more heat absorption [in the northern latitudes], what is that going to do to the nearby land ice? For instance, the Greenland ice sheet is very near to the area we're talking about. Will we see a more rapid melting? ... We're already seeing a substantial speed-up in the melt of both the Greenland and the west Antarctic ice sheets, it would appear, and so scientists are pretty worried about that because over a fairly long time period it could be that we're going to get 20, 30, possibly even more feet of sea level rise from the melting of those ice sheets."

On how often he feels it's necessary to quote climate change skeptics

"I quote the climate skeptics or deniers — whatever term you prefer — when they're relevant. So when I'm doing a piece about the science itself and what the latest scientific findings are, especially if that's a short piece, I don't necessarily feel obliged to quote the climate skeptics the same way that if you were doing a story about evolution, a New York Times reporter wouldn't feel obliged to call up a creationist and ask them what they think. On the other hand, the climate skeptics are politically relevant at this point in American history [in a way that] the creationists are not, for example. So we have a fair chunk of the Congress ... that sees political traction right now in questioning climate science or purporting not to believe it, so in a political story or in a longer story, I usually do give some amount of space to the climate skeptics."

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. You might remember the scorching heat wave that seized many areas of the U.S. last year or the deadly tornadoes that ripped through several states or the widespread coastal damage inflicted by Hurricane Sandy. Are these harsh weather events connected to global warming or simply the random violence nature sometimes visits upon us?

That's one of the questions considered by our guest, New York Times reporter Justin Gillis in his series "Temperature Rising," which focuses on the central arguments in the climate debate and examines the evidence for global warming and its consequences. Justin Gillis is an environmental reporter working at the Times science desk. In 2011, he won Columbia University's Oakes Award for Distinguished Environmental Journalism. He previously covered genetics and biotechnology for the Washington Post. Gillis spoke with FRESH AIR contributor Dave Davies.

DAVE DAVIES, HOST:

Well Justin Gillis, welcome to FRESH AIR. You know, it's a question that you hear in comedy routines, you know, just how hot is it. It's a question that you addressed in a recent piece about temperatures in the United States in 2012. How hot was it?

JUSTIN GILLIS: Well, 2012 was the hottest year in the historical record in the United States. They've now - the thing to understand about that is for thorough coverage of the whole country, the lower 48 states, our records go back to 1895, which of course is not that far back in time. But within that record we can say 2012 was the hottest year ever by about a full degree Fahrenheit over the previous record year, which was 1998. So that's a pretty big jump to occur in one year.

DAVIES: And if you kind of look back over the last 15 or 20 years, is there a clear trend?

GILLIS: Well globally there's certainly a clear trend. And within the United States, there's a trend of rising temperatures. There's a regional pattern to it. For instance, the Southeast has not warmed up as much as some of the parts of the country. But overall, both globally and in this country, the temperatures are rising, no question about that.

DAVIES: You also wrote about extreme weather episodes. Do you want to mention some of those and kind of tell us what we might know about their potential relationship to climate change?

GILLIS: Well, we've certainly had some remarkable weather in the last few years, weather extremes. People will remember the really intense drought from last year, for example, that did so much harm to the corn crop in the Midwest. We've had spectacular examples of cases of tornadoes, you know, such as the one that destroyed Joplin, Missouri. We seem to be living through this period of intensified and heightened weather extremes.

Now the truth is that scientists are - the common question that people ask on the street is: So is this climate change? And scientists have a bit of a hard time with that. For many of these kinds of weather extremes, we don't have particularly good statistics going back that many decades, for example. And so it's hard to say, in the case of tornadoes for example, we just don't have a very clear picture of what's developed over a long time.

With some types of extremes, though, climate science is fairly clear that there's a relationship between those extremes and the ongoing climate change. For example particularly with heat waves, you know, theory and evidence predicts that there will be a change in the distribution of heat extremes as the climate warms up, and that seems to be happening.

In addition, in some parts of the world, at least, there seems to be a rising trend of heavy rains or heavy precipitation, a rising percentage of precipitation falling in these short - these heavy bursts. That seems to be also related to climate change. So I would say overall it's an ongoing struggle for the scientists to puzzle out which of these things are linked and which ones aren't.

And of course the real question is how is the statistical likelihood of any given type of event changing in a changing climate. That's just ongoing research to puzzle that out.

DAVIES: I don't know if this is easy to explain or not, but why would the kind of climate change we're seeing result in short, heavy bursts of rainfall?

GILLIS: Well, the most basic reason is that the air is getting moister, and we've actually detected that scientifically. It sort of stands to reason that when things are hotter, there's going to be more evaporation at the surface of the ocean and more ability of the atmosphere to hold extra moisture. And that is indeed what we see.

And so eventually of course that moisture has to rain out and return to the surface of the Earth, and so the basic theory of climate change predicts that in a hotter climate, we will see an intensification of what's called the hydrologic cycle, and it appears that that's already happening. We're beginning to see that and beginning to detect that.

It has not been detected everywhere on the planet yet, and in fact in some places the statistics are just not good enough, the past statistics are just not good enough that we'll be able to detect it. But we do have places, and the United States is one of them, where we seem to be seeing this pattern already of heavier precipitation.

DAVIES: You know, one of the things that climate skeptics say is that if you look back over the long view of the Earth's history, you see variations in temperature, and there are ice ages, and there are periods of warming. And I know you've looked at how scientists have looked at past temperatures and rates of change of temperature. How does what we're seeing now compare to the historic record?

GILLIS: The way the skeptics, the climate skeptics or climate deniers, whatever you want to call them, tend to pose this is, well, there have been big changes in the climate of the Earth in the past; therefore, we humans can't possibly be causing any change in the climate. And that, of course, does not logically follow. It's true that there have been big changes in the climate in the past, that were purely natural and had nothing to do with human activity. You can't leap from that to, well, what we're doing now is going to have no effect. That's just a sort of irrational leap of logic to make, really.

One of the ways that we are trying to get a handle on what's likely in the future is to look at what's happened in the past. For example we can look in the past at the level of carbon dioxide in the atmosphere. I mean, we can measure that directly for about the past 800,000 years from bubbles trapped in air in the ice in Greenland and Antarctica.

And what you see is this very, very close association, relationship, between the amount of carbon dioxide in the atmosphere and the temperature of the planet. And so that's one of the things that leads scientists to say boy, if we put a huge amount of carbon dioxide in the air really rapidly, which is what we're doing, that's going to lead to an increase in temperature.

We do know, Dave, that there have been rapid changes in climate in the past that were, again, purely natural. This event, the current period that we're living through in which on a geological time scale we're causing an essentially instantaneous, very large increase in carbon dioxide in the atmosphere, there appears to be no real precedent for that in the geological record of the Earth as far back as we can look.

DAVIES: And when you say there have been periods of rapid temperature change in the past, we mean rapid, what, like over hundreds of years?

GILLIS: Well, rapid to a scientist would be on the geological time scale, would be sort of a few thousand years, actually. So, you know, as I say, on that time scale, geology, what we're doing is essentially instantaneous.

DAVIES: OK, so - and what implications does that have for, you know, the rest of the planet to adjust, you know, plant and animal life?

GILLIS: Well, we don't really know. When you look at the history of the Earth, there have been - sort of depending on how you count - six mass extinctions in Earth history. One of the theories about what causes them is that when things change too rapidly for species to adjust - you know, so, the theory would be that there's a speed limit, you might call it, on the rate of evolution or the rate of ecosystems adapting to changes in the climate.

And if you get too rapid a change, I think a lot of biologists would tell you, you're putting species at risk, or critters at risk, essentially. And so the theory, unproven, is that as we cause this probably fairly large change in the Earth's climate as a consequence of industrialization and the release of greenhouse gases, we will put so much stress on the ecology that a whole lot of organisms just won't be able to keep up.

Now what that implies for the way the world looks in 100 or 200 years, I think, nobody really has any great certainty about that. People are struggling with it.

DAVIES: We're speaking with Justin Gillis. He is an environmental reporter on the science desk of the New York Times and recently wrote the "Temperature Rising" series in the paper. We'll talk more after a break. This is FRESH AIR.

(SOUNDBITE OF MUSIC)

DAVIES: You're listening to FRESH AIR, and our guest is Justin Gillis. He's an environmental reporter for the New York Times, recently completed the "Temperature Rising" series, which examines central arguments in the climate debate.

You wrote, in September, about new data on the rate of melting of ice in the Arctic. What are we finding?

GILLIS: Well, what we're seeing, Dave, is a fairly rapid, now, decline in sea ice in the Arctic. Now a lot of people tend to confuse sea ice and land ice, and it's pretty important to separate them. Melting sea ice does not cause sea level rise. So the sea ice is already floating and displacing its weight in water, the old Archimedes principal, if you remember that.

And so when the sea ice melts, that does not cause sea level rise. When land ice melts, on the other hand, such as in Greenland and Antarctica, that does contribute to a rising sea. What we're seeing right now is acceleration, apparently, in the level, the amount of summer meltback of the sea ice in the Arctic. Our master overview of how much sea ice there is in the Arctic only goes back to 1978, which is when we first put satellites in the air that could look at the sea ice.

So within that period, we saw a record low last year. In fact there's been about a - something like a 40-percent decline in Arctic summer sea ice over the time that we've been watching. It's a pretty dramatic change in the face of the Earth. So science is now trying to figure out, OK, what's that going to do now that we're replacing a white surface up in the Arctic with a dark ocean surface that absorbs more energy. Are we in sort of a feedback loop? They're fairly sure we are. That's going to warm the Arctic up.

DAVIES: The feedback loop meaning that white stuff used to reflect sunlight, now it absorbs it and heats the oceans?

GILLIS: That's right. Some listeners might have heard the term albedo, and what that means, the albedo of the planet is its reflectivity. And one of the things that keeps the poles cold is that they're white, and therefore they reflect a tremendous amount of sunlight back to space. When you replace that white surface with a dark surface, that absorbs more of the sun's rays, and it just warms up more.

And so you get a little bit of warming, more absorption of heat. That causes more warming, and so you get what's known as a feedback loop that can cause the poles to warm up a good bit faster than the Earth as a whole. And that is indeed what we see happening.

So this situation with sea ice, I have to say, is - I mean, the scientists years ago, in fact more than 100 years ago, first predicted that this would happen, that we'd see a differential warming in the Arctic. But it is happening faster than they expected, and it's an example of potentially nasty surprises that are waiting for us as climate change unfolds.

The big question right now is as we get less and less sea ice in the summer, more and more heat absorption up there, what's that going to do to the nearby land ice. For instance the Greenland Ice Sheet is very near to the area we're talking about. Will we see a more rapid melting? For instance, you could imagine sort of more, warmer rain falling on the Greenland Ice Sheet as a result of the decline of the sea ice. Will we see more melting of the ice sheet?

In fact we're already seeing a substantial speed-up in the melt of both the Greenland the West Antarctic Ice Sheets, it would appear. And so scientists are pretty worried about that because over a fairly long time period, it could be that we're going to get 20, 30, possibly even more feet of sea level rise from the melting of those ice sheets.

DAVIES: So the melting of the land ice will contribute to sea level rise, unlike the melting of the ice in the ocean?

GILLIS: No question about that, and in fact the ocean is rising already. Many people know this. It's gone up about eight inches or so in the last century. That doesn't sound like much, but if you can imagine a very gently sloping shoreline, even eight inches of sea level rise has meant a whole lot of erosion. And in fact people have spent billions of dollars along the coastlines of the United States battling erosion already.

Now we're trying to understand, well, how much more sea level rise are we going to get over how long a period? The essential question is really how fast will this unfold. And a lot of scientists lately have been coming to the conclusion that we could fairly easily see three feet or so of sea level rise in the coming century and, you know, possibly as much as six feet.

So if we get that much, that's going to start to become a pretty serious problem.

DAVIES: You know, it struck me that one of the challenges that you face in doing this kind of reporting is, if you, for example, as you did in September, have a story about new information about the rate of polar ice melting, I mean, I think the reaction to a lot of editors would be: didn't we just run a story on that? Doesn't everybody know the polar ice is melting? And then the story gets to be on page B6. How do make the case that no, this is still front-page news?

GILLIS: Well, the most fundamental problem of all, I think, for a reporter trying to cover this, is much of the science that tells us there's a problem, that you need to understand, to know that there's a problem, was done 20 and 30 years ago. The last few decades of research have been trying to fill in the gaps and understand OK, exactly how much of a problem. And, you know, we haven't really narrowed the uncertainties all that much.

And so it's absolutely true that when you confront this on a, sort of, day-to-day basis, you're constantly wrestling with the question: didn't we already know that? And, I mean, my approach to this has been to say, well, if I back up and figure out a way to take deeper dives in and not just write about, you know, the polar ice melting on page, you know, A20 or whatever, but try to do somewhat deeper dives into the overall science and what it means, that people will respond to that.

And that seems to have worked over the past few years.

DAVIES: There's a website that calls you a warmist, and, you know, there are climate skeptics out there that treat climate change as a scientific hoax. Now I've heard from a lot of credible journalists that among serious climatologists that there is consensus that the climate is changing and that human activity is, you know, contributing to or causing it.

But as a journalist, how do you deal with this? I mean, how often do you feel like you should quote climate change skeptics in your stories, even if you feel like, you know, they're really outside the credible mainstream?

GILLIS: Well, it's important to understand, first of all, Dave, that I mean this is a robust, healthy science. And within the scientific mainstream, there is a considerable range of views about just exactly how much risk we're running. There's probably - there's certainly a range of views about what the likely ultimate consequences are going to be in terms of temperature.

When I look at the scientific majority, the scientific mainstream, I would say that, as a group, they fear this is going to be pretty bad. They don't know exactly how bad it's going to get, and they don't know how fast it's going to get that way - which might be the ultimate question.

Now to answer your question, my approach to this is I quote the climate skeptics or deniers, whatever term you prefer, when they're relevant. So when I'm doing a piece about the science itself and what the latest kind of scientific findings are, especially if that's kind of a short piece, I don't necessarily feel obliged to quote the climate skeptics in the same way that if you were doing a story about evolution, a New York Times reporter wouldn't feel obliged to call up, you know, creationists and ask them what they think.

On the other hand, the climate skeptics are politically relevant in a way that, at this point in American history, the creationists are not, for example. So we have a fair chunk of the Congress, for example, that sees political traction right now in questioning climate science or purporting not to believe it. And so in a political story or in a longer story, I usually do give some amount of space to the climate skeptics.

Now I try not to overdo that. As journalists, we don't want to fall into this trap of what's called false balance, where you take two positions that have completely different weight of evidence and treat them as equal. So sort of in no story am I treating the climate denier position as equal to the mainstream scientific consensus, because I don't think it is. I mean, I think you look at the weight of evidence, and there's sort of just a huge pile of it in favor of the mainstream science and not very much published scientific evidence at all that really stands up to say this is not a problem.

DAVIES: So you'll quote the climate skeptic, but you make clear where the mainstream scientific community is.

GILLIS: That is exactly what I try to do, yes.

DAVIES: Justin Gillis, it's been interesting. Thanks so much for spending some time with us.

GILLIS: Surely.

GROSS: Justin Gillis spoke with FRESH AIR contributor Dave Davies. Gillis is an environmental reporter for the New York Times. You'll find links to his articles and his "Temperature Rising" series on our website, freshair.npr.org. I'm Terry Gross, and this is FRESH AIR. Transcript provided by NPR, Copyright NPR.